Intrathoracic Tracheal Volume and Collapsibility on Inspiratory and End-expiratory CT Scans: Correlations with Lung Volume and Pulmonary Function in 85 Smokers

Abstract

To evaluate the correlations of tracheal volume and collapsibility on inspiratory and end-expiratory computed tomography (CT) with lung volume and with lung function in smokers. The institutional review board approved this study at each institution. 85 smokers (mean age 68, range 45-87 years; 40 females and 45 males) underwent pulmonary function tests and chest CT at full inspiration and end-expiration. On both scans, intrathoracic tracheal volume and lung volume were measured. Collapsibility of the trachea and the lung was expressed as expiratory/inspiratory (E/I) ratios of these volumes. Correlations of the tracheal measurements with the lung measurements and with lung function were evaluated by the linear regression analysis. Tracheal volume showed moderate or strong, positive correlations with lung volume on both inspiratory (r = 0.661, P < .0001) and end-expiratory (r = 0.749, P < .0001) scans. The E/I ratio of tracheal volume showed a strong, positive correlation with the E/I ratio of lung volume (r = 0.711, P < .0001). A weak, negative correlation was found between the E/I ratio of tracheal volume and the ratio of forced expiratory volume in the first second to forced vital capacity (r = -0.436, P < .0001). Also, a weak, positive correlation was observed between the E/I ratio of tracheal volume and the ratio of residual volume to total lung capacity (r = 0.253, P = .02). Tracheal volume and collapsibility, measured by inspiratory and end-expiratory CT scans, is related to lung volume and collapsibility. The highly collapsed trachea on end-expiratory CT does not indicate more severe airflow limitation or air-trapping in smokers.